350 Dr. E. B. Roll— On Fossil Sponges. 



proceeds from the centre, and growth takes place by additions to 

 the thickness of the rays and at the points, and the occurrence of 

 radiate spicula in the same individual sponge of all sizes, from the 

 matured condition down to extreme smallness, always preserving the 

 radiate form, is entirely against the view of M. Etallon. If union 

 ever takes place, it is probably the result of fossilization, in cases 

 where the points of the rays are in contact, and it is then brought 

 about probably either by adventitious deposit, or in the replacement 

 of the original structure the mineral which has infilled the mould 

 has run together. 



Nevertheless the labours of M. Etallon are a move in the right 

 direction, and it appears probable from his research that by a careful 

 investigation of the structural details of the fossil sponges, it may 

 be possible ultimately to arrive at results which may lead to an 

 arrangement of the species and genera more suited to the require- 

 ments of the day than the artificial systems of D'Orbigny and 

 De Fromentelle. The time, however, is probably not yet come for 

 this to be attempted, the more especially as the arrangement of the 

 recent species is far from being settled,' 



V. — Two conclusions are suggested by the foregoing remarks : — 

 1st, that the present state of the fossil sponges affords no certain 

 indication of their condition during life ; and 2nd, that in the 

 differentiation of the genera and species, the same principles must be 

 kept in view in the fossil as in the recent sponge. Some of the 

 oldest fossil sponges were as highly organized apparently (if the 

 term is admissible to these humble forms of life) as those of the 

 present day, as for instance the Protospongia of the Lingula Flags 

 and Ludlow Eocks,^ the Silurian Ischadites, and the Devonian 

 SpJicerospongia tesserata. The Frotospongice, in fact, belong to that 

 general type of cyathiform sponges, formed of elongated vertical and 



^ These " Notes" were written in the year 1866. 



2 Two undescribed species of this genus occur in the Lower Ludlow rocks of 

 Leintwardine, for one of which I propose the name of P. Ludense, and for the other 

 P. maculceformis. In P. Ludense the sponge has the figure of a horn slightly curved, 

 and attains a height of 10 or 12 inches, and a transverse diameter (in its compressed 

 state) of 4 or 6 inches. It consists of vertical and transverse fibres, which intersect 

 each other obliquely at the base, but become more or less horizontal as the sponge 

 enlarges ; it is not evident, however, whether these fibres were united at the points of 

 intersection, or simply apposed. The fibres which emanate from the base ascend to 

 the summit, but as the sponge enlarged other fibres became intercalated, and scattered 

 stellate (four-rayed ?) spicula occur in the interspaces. In all the specimens hitherto 

 met with the sponge is completely fiattened, but its original cup-shaped figure is 

 shown in a specimen in the Ludlow Museum, in which a thin plate of compressed 

 sediment which filled the cavity exhibits the fibres on either side ; and in the P. 

 fenestralis of the Lingula Flags, the same can be ascertained by making transverse 

 sections, when the cut ends of the rods are shown ranged in parallel rows on either 

 side of a lamina of the matrix which occupied the cavity, reduced to a mere plate by 

 compression. The other species, P. maculceformis, occurs as semi-circidar or serai-oval 

 stains on the surface of the Lower Ludlow shales, about \\ inches in height and an 

 inch in transverse diameter. As in the former species, it consists of extremely delicate 

 vertical and transverse fibres, with a few stellate spicula in the interspaces. So thin 

 is the fossil that it might readily be mistaken for mere vegetable stains, unless the 

 fibres are especially sought for with a magnifying glass, and its cup-shaped form 

 is inferred only from the type to which the sponge evidently belongs. 



